Prior to the 1950's fatty acid soaps were the primary ingredients in laundry detergents. While the fatty acid soaps created problems in the presence of hard water, they left fabrics coated with a microscopic residue of fatty soap that left the fabric with a lubricated soft feel. With the advent of synthetic detergents, there developed a need for laundry products that would restore the soft, fluffy feel that is desirable on fabrics. Rinse cycle fabric softeners filled this need. Liquid fabric softeners have been used for many years in both household and commercial laundries.
Commercial and industrial laundries use harsh, highly alkaline detergents to wash fabrics. These harsh detergents thoroughly scour the fabric fibers which results in a rough, scratchy irritating feel after the fabric is dried. The irritating feel to the fabric is especially pronounced with cotton fabrics, but also is found with polyester and cotton/polyester blends. Fabric softening and conditioning agents are applied to the fabric to reduce the harshness by forming a layer of fatty organic substance that has a soft feel. Acidic materials can be incorporated into softeners or conditioners to neutralize excess alkalinity that can contribute greatly to the harsh feel of fabrics and that can damage the fibers when heated at the high temperatures typical of industrial or institutional laundry dryers.
Fabric softeners have usually contained cationic surfactants, especially quaternary ammonium compounds. Fabric softeners have been made in liquid and solid forms and as coatings on small polymeric spheres. The acidified liquid softeners are usually quite dilute by virtue of the low gel forming concentration characteristic of quaternary ammonium compounds and cationic surfactants generally in aqueous acid diluents.
Fabric softening compositions applied in the washing machine have traditionally been liquid products either added by hand or automatically pumped into the final rinse cycle. When used in institutional or industrial applications, acids are often added to the softening composition to neutralize the sodium hydroxide, potassium hydroxide or any other highly alkaline components that carry through the rinse cycles. These products are corrosive by virtue of their acidity and can damage vehicles, equipment, facilities or tissue if spilled while shipping or handling.
U.S. Pat. No. 4,497,718 to Neiditch et al. describes a dilute aqueous liquid softener with 0.5 percent to 10 percent cationic surfactant. This particular softener includes a stilbene sulfonic acid as a fluorescent whitening agent. Weak organic acids, such as citric acid and benzoic acid, are added to adjust the pH to be between 3 and 6. U.S. Pat. No. 4,114,177 to Minegishi et al. describes a fabric softener composition with anionic surfactants and quaternary ammonium salts. The softener composition can be used in the form of a liquid. U.S. Pat. No. 4,308,024 to Wells discloses a liquid fabric softener that has a relatively insoluble cationic detergent, a monocarboxylic acid and a relatively water soluble cationic detergent or a cationic polymer. U.S. Pat. No. 4,427,558 to David describes a fabric softener with a cationic surfactant especially quaternary ammonium salts, urea and calcium soap. The material is preferably formed into a powder and can include detergent compounds.
U.S. Pat. No. 5,093,014 to Neillie discloses the use of amphoteric compounds in the production of liquid fabric softeners. The amphoteric compounds include tertiary amine oxides that are monomethyl. The preferred amine oxides contain two carbon chains with at least 14 carbon atoms. The compositions must contain a coactive material which include cationic, nonionic and semipolar surfactants to prevent phase separation. Great Britain Patent 1,260,584 similarly discloses the use of tertiary amine oxides with two long alkyl chains with 8 to 24 carbon atoms used as fabric softeners.
The potential softening properties of certain nonionic materials have been recognized before. U.S. Pat. No. 4,128,484 to Barford et al. discloses a fabric softener containing a fatty alkyl ester of a polyhydric alcohol. These softeners contain at least 5 percent cationic surfactant. The presence of the cationic surfactant is important in creating the softening effect of the nonionic fatty ester. U.S. Pat. No. 4,237,016 to Rudkin et al. also describes softeners (conditioners) with a nonionic softening agent. The nonionic softeners are fatty esters or fatty alcohols in esters with smaller chained carboxylic acids. The nonionic softeners are present in concentrations of 2 to 10%. The composition also contains 0.3% to 4% cationic surfactant such as quaternary ammonium salts and from 0.05% to 0.5% polymeric cationic salt.
Fabric softeners or conditioners can also be deposited in thin films on insoluble substrates such as spheres or fibers. These softeners are typically for use in a dryer rather than a washer where the heat of the dryer softens or melts the softening composition so that it can transfer to the article of clothing when it comes into contact during the tumbling process. U.S. Pat. No. 4,057,673 discusses a softening composition that includes a plasticizer. The fabric softeners include nonionic, anionic or cationic surfactants. Suitable nonionic surfactants are stated to include fatty esters, fatty amides, fatty ethers, fatty and certain polymers. Plasticizers were found to improve the transfer of the softener to the fabric.
For institutional applications the handling convenience of solid cast cleaning compositions is a significant consideration. U.S. Pat. No. 4,769,159 to Copeland describes a solid cast fabric softening product. These solid softeners include a cationic surfactant, especially a quaternary ammonium salt, and a dicarboxylic acid. The production of the solid product is based on the melting of the cationic surfactant.
Combination products that involve both detergent and a softener are also available. For these products, a relatively neutral pH would typically be used to eliminate or reduce the need to add a later product to adjust the pH. U.S. Pat. No. 4,233,167 to Sramek discloses a liquid detergent with softening and brightening properties. Nonionic surfactants are used for their cleaning properties and a quaternary ammonium salt is used for its softening ability. A long list of suitable nonionic surfactants are given including tertiary amine oxides.
U.S. Pat. No. 4,268,401 to Meschkat et al. a liquid fabric cleaner that also softens. These compositions also contain a nonionic surfactant and a quaternary ammonium softener. The nonionic surfactants are preferably alkylpolyglycol ethers. U.S. Pat. No. 4,547,300 to Lareau describes a product with a nonionic surfactant, a cationic softener and a optical brightening agent. A range of suitable nonionic surfactants are described as including those generally known in the art with certain preferred surfactants enumerated.
Quaternary ammonium chlorides (quats) have served as the major active ingredient in fabric softener formulations for many years and continue to be the primary material of choice for this application. Relevant quats have the structure [R.sub.4 N].sup.+ X.sup.-, where R can be any length hydrocarbon chain from C.sub.1 to C.sub.22 and X.sup.- is typically chloride or sulfate although other anions can be used. The hydrocarbon chain lengths can be and often are different for the four chains.
Variations in quaternary ammonium chloride composition over the years have been mainly to change the handling characteristics, e.g., viscosities, solubilities, or to change the chloride to sulfate to reduce corrosiveness. Particularly useful quats have substituents that are dimethyl difatty alkyl or trimethyl monofatty alkyl comprising the four R groups characterized by having four carbon atoms chemically bonded to the nitrogen. Imidazolines are also considered quat softeners under this definition.
Quaternary ammonium softeners have a very strong affinity for a surface on which they can absorb. If overused, the quaternary ammonium compound can build up on the fabric causing a property known as "waterproofing" which is undesirable because fabrics meant to absorb liquids will no longer absorb. Quaternary ammonium softeners, which contain large cations, can combine with some large anionic molecules and precipitate. Once precipated, they are no longer able to bind to the fabric and lose their softening ability.
Other materials have been used in liquid products to impart softness to fabrics, in addition to quaternary ammonium salts. U.S. Pat. No. 3,984,356 to Graham describes the use of a dicarboxylic acid salt as the softening agent in a combination laundry detergent and softener product. Mineral oil and paraffin wax emulsions also have been used to provide the lubrication resulting in the soft feel of fabric softeners.
Washer applied fabric softeners have been based on cationic compounds. Quaternary ammonium salts are recognized as some of the best softeners among these cationic compounds. While it has been recognized that nonionics can have softening properties when used in combination with some cationics, the use of washer based nonionic compounds as softeners has been quite limited. This is due to the perceived lack of adherence of nonionics to the fabric. In dryer based applications where melted or softened compounds transfer by contact with the fabric, nonionics and cationics are more readily used.
Commercial or industrial laundries typically use chlorine bleach, i.e., aqueous sodium hypochlorite solutions, to remove stains, whiten linens and sanitize. With the typical washing protocol designed to save water, there will usually be a measurable amount of hypochlorite left in the fabric even after several rinses. The presence of hypochlorite can be detrimental to fabrics because it chemically reacts with the fabric when subjected to the high temperatures in commercial dryers. The result of the reaction with the fabric is to weaken the fabric or produce holes which shorten the useful life of the fabric.
The laundry industry has used "antichlors" to destroy remaining hypochlorite bleach and therefore to reduce the damage to the fabric. Antichlors are reducing agents, usually of the sulfite family, i.e., sulfite, thiosulfite and metabisulfite salts. The sulfites generate an obnoxious odor when acidified.
Consequently, these antichlors have not been added to liquid fabric softeners containing acids. It would be advantageous to have a compound to reduce hypochlorite in an acidic fabric softening product.